Electric power substations for use at very high voltages occupy a large space on the ground as a result of the large separation required between live components of units such as power transformers, circuit-breakers, isolating switches and busbars.
To provide an adequate level of flexibility in operation, more units must be included in the substation than the strict minimum requirement or other measures must be taken which also tend to increase the area occupied by the substation. For example, to enable circuit-breakers to be serviced without interrupting the distribution of electric power, certain types of substation comprise three circuit-breakers per pair of line outlets (the so-called "one and a half circuit-breaker" configuration). Other types of substation comprise circuit-breakers connected to two sets of busbars. A third set of "transfer" busbars is provided to compensate for failure of any circuit-breaker. Also known are so-called ring or loop installations in which a significant area is wasted inside the ring or loop.
To provide maintenance personnel with safe access to the circuit-breakers it is necessary to provide around each circuit-breaker a region wherein access to the circuit-breaker is protected against the effects of the very high voltage. This further increases the area on the ground occupied by a very high voltage electric power substation.
It is known to reduce the size of electric power substations for use at very high voltages by using smaller equipment housed in sealed metal enclosures filled with an insulating gas. This solution significantly increases costs, however.
Another known method of reducing the area on the ground is to use a multilevel arrangement, with three levels, for example. The first level is the floor plane. The circuit-breakers are in the second level which is above the floor plane. Vertical isolating switches are also placed on the second level with the busbars on the third level. The isolating switches are fitted with articulated arms in a pantograph configuration. When the isolating switch is open-circuit, the arms are folded in a vertical plane and their vertical projection onto the floor plane extends a significant distance beyond the perimeter of the isolating switch proper. As these arms may be live even when the isolating switch is open-circuit, the use of this type of isolating switch means that the distance between the busbars must be increased, as it is not always possible to arrange the isolating switches such that the vertical plane containing the folding arms is parallel to the busbars.
The present invention is intended to provide an electric power substation for use at very high voltages occupying a surface area on the ground which is less than in the case of the prior art substations referred to above.